Frequently, assemblies of electronic components providing similar or identical functions are fabricated in modular units and located together in groups, for example in switch rooms, in order to facilitate the adjustment, testing, and repair of the assembly units, or their replacement as required. Typical of such units are component assemblies referred to as "terminal blocks" which, depending upon the contained components and wiring mode, are used for current attenuation through included resistor elements; the generation of "sealing currents" which protect against corrosion by provision of a low amperage current; for the bridging connection of selected circuits, as well as other uses. Terminal blocks are widely employed in areas such as telecommunication, data transmission, power and utility distribution, for transmitting broadcast audio, and in a variety of additional areas. Very often, the sheer number of module located together results in space constraints which necessitate a high density arrangement of the units. Commonly this is accomplished by positioning the units in vertical, adjacent stacks, one over the other utilizing frame-like racks termed "distributing frames," which are positioned in parallel rows in the switch room. Sufficient vertical space is provided between the modules to allow access, particularly from the top, so that required procedures may be performed on the units.
In such arrangements the vertical stacks are typically so high, often eleven feet or higher, that a movable ladder must be provided, suspended from a supporting rail positioned parallel to, and in front of the distributing frames. In the case of assembly units located too high to be conveniently reached from the floor, the ladder is moved along the rail to the stack in which the assembly unit of interest is located, providing access to the unit.
While positioning of the modular assembly units as described results in economies of space, their close proximity makes their contained components vulnerable to damage. In the case of terminal blocks, for example, electric cables containing wires required for attachment to pins within the blocks are pulled along behind the rows, frequently resulting in injury to the contained components, especially to electrical connection pins located therein, when the blocks are uncovered. The pins can also be injured by the shoes of workers climbing the ladders, and uncovered pins provide a safety hazard to workers. Furthermore, while uncovered electrical assemblies positioned over each other in distribution frames are easier to work on than covered assemblies so positioned, uncovered lower assemblies are vulnerable to debris such as pieces of solder falling into them as a result of work on higher assemblies. Such contamination can easily result in electrical shorting of the components making up an assembly, leading to destructive damage and malfunction. In addition, uncovered assembly units tend to accumulate dirt, dust and other material adventitiously entering the assemblies, likewise involving the risk of damage to the units.
Although some electronic assembly units are provided with covers to protect their interiors, the removal of covers can involve the removal of fasteners, a relatively arduous task particularly in the cramped confines typically encountered in frames of the type described. In the case of another type of cover, velcro fasteners are provided to simplify removal and replacement of the covers; however, experience has shown that the covers frequently fall or are thrown to the floor, resulting in damage to them, and that they are never replaced.
It has also been proposed to provide hingeable protective cover structures, designed to allow access to housed electronic components. Such devices are shown, for example, in U.S. Pat. No. 3,299,323, which teaches a hinged cover attached to a box-like cabinet containing electrical chassis, and in U.S. Pat. No. 3,634,732, which illustrates a cabinet for housing electronic components such as printed circuits, and which includes a hinged cover member.
The hinged covers taught in the preceding patents are unsuitable for accessing the components in closely spaced assembly units from the top, however, particularly where the distributing frames holding the assembly units require a ladder closely positioned to the frames to reach the higher assembly units.